My oil furnace keeps making soot and cut off. When we clean out the soot it comes right back. Filter and nossle has been changed, I have 17 inches of oil in my 550 gallon tank. What could be the problem

The burner is not running properly and this is the reason for the soot. There is more to a oil burner than just installing a nozzel and changing the oil filter. Different oil burners combined with different size and configurations of combustion chambers need different types of nozzels with different degrees of spread to start with along with the oil pump pressure settings and air over/barometric damper adjustments.

It is also a good possibility the nozzel holder is cracked dumping raw fuel into the combustion chamber. This is just about all I have on the issue since I cannot see or be there to do the adjustments using the proper tools for the job.